408 THE STUB Y OF INSECTS. 



slightly with brown to a dark cinnamon color ; they are 

 bordered with black, and all the veins are edged with the 

 same color (Fig. 479). The fringe of the wings is spotted 

 with white, and the black border on the outer margin con- 

 tains a row of white spots. 



Fig. 479 — Rasilarchia a< chifipus. 



This species is remarkable for its resemblance to the 

 Monarch (Anosia plexippus, Fig., 469). But aside from the 

 structural characters separating the two subfamilies which 

 these butterflies represent, the Viceroy can be easily distin- 

 guished from the species it mimics by its smaller size, and 

 by the presence of a transverse black band on the hind 

 wings. 



It is believed that the resemblance of these two species 

 is not merely accidental, but is a result of the action of the 

 law of natural selection. The butterflies of the subfamily 

 to which the Monarch belongs (Enplceince) are exempt from 

 the attacks of birds. It is supposed that this exemption is 

 due to the possession by these butterflies of a disagreeable 

 odor. With such an odor the conspicuous coloring of the 

 butterflies is protective, the birds soon learning that such 

 butterflies are not fit for food. And it can be seen that these 

 birds will naturally leave undisturbed any other butterflies 



